Combined Geochemical Methods in Surface Exploration of the Senillosa Area, Neuquén Basin, Argentina
Larriestra, Fernando¹; Larriestra, Claudio¹; Lanussol, Daniel²; Gastaldi, Santiago³
¹Larriestra Geotecnologías S.A., Buenos Aires, Argentina.
²E&P Consulting, Buenos Aires, Argentina.
³Petrolera Pampa S. A., Buenos Aires, Argentina.
The following is an exploratory research of surface geochemistry in an area located 30 km west of Senillosa town, Neuquén province. It comprised a number of transects with equidistant sampling stations where soil samples were taken for microbial (buthanotrophic bacteria) and trace elements analysis. In addition, vegetation indexes were obtained as the Shannon Diversity Index (H) and Species Richness (S) at each sample station, and species coverage maps were obtained to seek for potential biomarkers of gas micro leakages. The results obtained from bacterial analysis show high background values (those less than 2500 cfu/g), while those corresponding to the blocks (structures north middle and south) were in the range of 2500 to 17500 cfu/g. The faulting associted anomalies cover up to 180000 cfu/g. Abnormally high background values could be due to the activity of deep petroleum systems that send gases from both source rock (Vaca Muerta and Molles Formations) and associated reservoirs.
Soil trace elements like vanadium, nickel, chromium and copper were appeared related to elevated blocks and faults and were associated with the oil generated in Vaca Muerta Formation whose main feature is the presence of vanadium, nickel and chromium and incidental elements such as copper, arsenic and zinc. In addition, mass spectrometric analysis performed on an oil sample from a well in the area also detected high values of vanadium.
These results together with vegetation analysis, soil gas and a possible biomarker plant species (Acantholippia seriphioides), were compared with digital processing of satellite images such as NDVI and Tassled Cap. The integration of geothermal gradients measured in wells geostatistically integrated with thermal images allowed the construction of a thermal gradient map. Those structures with higher thermal emission match with the anomalies mentioned above.
This research allowed to confirm the existence of active petroleum systems, some of them investigated before while others still remain unexplored. Areas of current and past microseeps were identified, setting new targets to explore.
AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012